The present invention generally relates to proteins, particularly a group of pregnancy-specific .beta.-1 glycoprotein-like proteins, the genes encoding them, and methods for their use.
Pregnancy-specific .beta.-1 glycoprotein (SP1 ) is found in the serum of pregnant women and has been isolated in pure form, as reported by Tatarinov and Masyukevich, Bull. Exo. Biol. Med. 69, 66-68 (1970). It is synthesized by the syncytiotrophoblast of the placenta and secreted into maternal serum, as studied by Bohn, Placental Proteins, pp. 71-18, A. Klopper and T. Chard, editors (Springer Verlag, N.Y. 1979), becoming detectable during the first two to three weeks of pregnancy and increasing as pregnancy progresses to levels of about 200 to 400 .mu.g/ml, as reported by Tatarinov and Masyukevich Bull. Exp. Biol. Med. 69, 66-68 (1970) and Lin, et al., J. Clin. Invest. 54, 576-582 (1974).
Even though the placental origin of human SP1 is well established, low levels of this protein can be detected in serum of the normal male and female by radioimmunoassay. The extraplacental source of human SP1 has not been identified. Ectopic production of SP1 by cultured human skin fibroblasts and normal brain cells has been reported by Heikinheimo, et al., J. Clin. Endocr. Metab. 51, 1432-1436 (1980); Rosen, Pregnancy Proteins, pp. 223-234 (1982); and Chou, Oncodevelop. Biol. Med. 4, 319-326 (1983), but the cause is not known.
As first reported by Bohn, Blut 24, 292-302 (1972), SP1 isolated from placenta consists of a single polypeptide chain with an N-terminal histidine, having a molecular weight of 90,000, of which 30% is carbohydrate. Several subsequent studies have indicated that this "protein" is actually a heterogeneous mixture of several components. There is a wide discrepancy of reported molecular weights for human placental SP1. Values determined by gel filtration, ultracentrifugation and SDS-PAGE vary from 110,000 to 42,300, respectively. Carbohydrate varies from 28 to 32%. As reviewed by Bischof, Contri. Gynecol. Obstet. 12, 6-92 (1984), electrophoretic mobility ranges from .alpha., .beta., to gamma. Genetic variants of SP1 have also been reported in both normal and abnormal pregnancies as well as in tumors. It has been suggested that these variants involve a change in protein size or sequence.
cDNA sequences encoding placenta-specific SP1, having slight differences in sequence at the 3' end, were reported by Watanabe and Chou in J. Biol. Chem. 263, 2049-2056 in 1988, and Streydio, et al. in Biochem. Biophys. Res. Comm. 154(1), 130-137, (1988). Monoclonal antibodies to human SP1 have also been reported to have different and unique specificities and affinities, although it is not known if the antigenic determinants are on the same or different proteins.
SP1 determinations have great potential clinical application, even though the function of SP1 is still not known. The medical relevance of SP1 in a number of situations has been extensively investigated. The most important use of SP1 is for monitoring various conditions, both normal and pathological, during pregnancy, reviewed by Bischof (1984). SP1 measurements have also shown promise for the diagnosis and monitoring of trophoblastic and some nontrophoblastic tumors, as described by Sorensen, Clin. Chim. Acta 121, 199-208 (1984).
Despite the potential, SP1 has not been well utilized in clinical medicine because of the lack of reliable quantitation methods. At present, the majority of the SP1 assays depend on antiqen-antibody interaction, dependent on the nature of the SP1 molecule and on the specificity of the antibody involved. Heterogeneity of the SP1 molecules decreases the reliability of these immunoassays.
It is therefore an object of the present invention to provide the nucleotide sequences and structure of a group of several SP1 proteins.
It is a further object of the present invention to provide a method and means for producing extremely pure SP1 proteins for pharmaceutical use.
It is another object of the present invention to provide a methods and means for producing monoclonal antibodies for quantitating the different species of SP1 and for improving assays for CEA by eliminating cross-reactions with SP1-like proteins in non-placental tissues.
It is a further object of the present invention to provide methods and means for use in pregnancy assays and in detection and monitoring of trophoblastic and some non-trophoblastic tumors
It is still another object of the present invention to provide reagents for use in preventing fetal rejection, in inducing rejection of the embryo in therapeutical procedures, and in improving the transfer of immunoglobulins into the fetus.